Yes if f- give you 1 than you would put it in the space that has nothing there.. and you will she the right answer.
Let the number be x
Equation:
12 + 5x = -3
Answer: The equation is 12 + 5x = -3
Solve it:
5x = -3 - 12
5x = -15
x = -15 ÷ 5
x = -3
Answer: The number is -3.